Adding a module, when an earlier version of that module is also bundled, doesn't work right

I'm running 1.8 as a war in tomcat. I've installed reportingcompatibility-1.5.5-SNAPSHOT.

Occasionally it resets itself to 1.5.4.1 (which must be bundled, though I haven't verified yet).

If I go to manage modules and remove the 1.5.4.1 reporting compatibility module, then try to add the 1.5.5-SNAPSHOT version, it fails, telling me that it's already associated with a loaded module (or something like that).

If I then restart tomcat, it will come up showing 1.5.5-SNAPSHOT in the manage modules screen, but it's stopped.